Depends on the metric IMO. There's a ton of use you can get out of forecasting and seasonality for anomaly detection, but you need data going back for that to have any chance. Many relevant operations metrics exhibit three levels of seasonality: daily (day/night) weekly (weekday/weekend) and annual (holidays, superbowls, media events). Being able to forecast network traffic inbound on a switch to find problems would require you to have 1y of data, effectively. You _might_ be able to discard some of the data but you'd lose some of the predictive capacity for say, the Super Bowl.